Variable magnification optical system, imaging optical device, and digital appliance

ABSTRACT

A variable-magnification optical system has five lens groups, namely, from object side, positive, negative, positive, positive, and negative lens groups, and achieves magnification variation by varying all axial distances between the lens groups. Focusing is achieved by moving the fourth lens group in optical axis direction. Vibration correction is achieved by moving all or part of the fifth lens group perpendicularly to optical axis. Fulfilled are formulae 4.0&lt;|f1/f2|&lt;6.0, 1.0&lt;f4/f1&lt;1.5, and 2.0&lt;|f4/fv|&lt;4.0, f1 representing a focal length of the first lens group, f2 a focal length of the second lens group, f4 a focal length of the fourth lens group, and fv a focal length of the vibration correction group.

This application is based on Japanese Patent Application No. 2013-122084filed on Jun. 10, 2013 and Japanese Patent Application No. 2013-203918filed on Sep. 30, 2013, the contents of both of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable-magnification opticalsystem, an imaging optical device, and a digital appliance. Moreparticularly, the present invention relates to, for example, a compactvariable-magnification optical system suitable for use in aninterchangeable-lens digital camera that takes in an image of a subjectwith an image sensing device, an imaging optical device that outputs animage of a subject taken in with such a variable-magnification opticalsystem and an image sensing device in the form of an electric signal,and a digital appliance having an image input function, such as adigital camera, that is provided with such an imaging optical device.

2. Description of Related Art

In recent years, mirrorless interchangeable-lens digital cameras, whichhave no swing-up mirror as are provided in single-lens reflex cameras,have found acceptance among users and gained an increasingly largemarket. Some mirrorless interchangeable-lens digital cameras cannotadopt phase-difference AF (automatic focusing), which is the mainstreamin conventional single-lens reflex cameras; those cameras have to adoptso-called contrast AF, whereby focusing is achieved by scanning for thehighest-contrast position with a focusing lens group.

Here, the weight of the focusing group matters. With phase-differenceAF, the amount of movement of the focusing group needed to achievefocusing can be calculated based on information from an AF sensor, andthus the focusing group can be moved according to the calculated amount.By contrast, with contrast AF, only the contrast values at given momentscan be obtained from an AF sensor; thus, while the focusing group ismoved, and meanwhile how the contrast value varies from one moment toanother is read, the highest-contract position is searched for toachieve focusing. Thus, the amount of movement of the focusing groupneeded to achieve focusing is fax larger with contrast AF than withphase-difference AF.

From the above perspective, in a variable-magnification optical systemdesigned to be compatible with contrast AF, a reduced weight of thefocusing group is a great advantage (for example, see Patent Documents 1and 2 identified below). In conventional variable-magnification opticalsystems for use as interchangeable lenses for single-lens reflexcameras, for example, a positive-negative-positive-positive zoom type asdisclosed in Patent Document 3 and apositive-negative-positive-negative-positive zoom type as disclosed inPatent Document 4 are the mainstream. However, from the aboveperspective, the focusing groups in the lens systems disclosed in PatentDocuments 3 and 4 are not satisfactorily light. Thus, new opticalsolutions are being sought.

-   Patent Document 1: Japanese Patent Application Publication No.    2012-14005-   Patent Document 2: Japanese Patent Application Publication No.    2012-225987-   Patent Document 3: Japanese Patent Application Publication No.    2009-271471-   Patent Document 4: Japanese Patent Application Publication No.    2011-221422

In the zoom lens system disclosed in Patent Document 1 mentioned above,the second lens group is used as a focusing group, and is notsatisfactorily light as a focusing group. In the zoom lens systemdisclosed in Patent Document 2, the fourth lens group which is composedof a single lens element having a negative optical power is used as afocusing group, and is significantly light as a focusing group. Here,the second lens group in an ordinary positive-negative-positive-positivetype zoom lens system is divided into a positive, a negative, and apositive sub groups to set apart the focusing group. In a zoom lenssystem that includes, from the object side, a positive, a negative, apositive, . . . lens group, magnification variation action ascribable tovariation in the distances between the first and second lens groups andbetween the second and third lens groups accounts for the large part ofthe magnification variation action of the entire optical system.However, in the construction disclosed in Patent Document 2, as a resultof the second lens group being divided, the second to fifth lens groupsproduce a low zoom ratio, and thus the sixth lens group needs to producethe large part of the desired zoom ratio. Obtaining the desired zoomratio, therefore, requires an increased total optical length at thetelephoto end.

In the lens systems disclosed in Patent Documents 3 and 4, a reductionin the weight of the focusing group may be achieved by performingfocusing with a lens group located to the image side of the third lensgroup which has a small lens diameter. However, in the lens systemdisclosed in Patent Document 3, the fourth lens group serves forvibration correction, and therefore, arranging a focusing mechanismclose to the fourth lens group results in a drive mechanism for focusingand a drive mechanism for vibration correction being arranged closetogether, which can be disadvantageous from the viewpoint of spaceefficiency

Conventionally, a vibration correction function is incorporatedexclusively in comparatively telephoto-oriented lens systems. However,as zoom lens systems are designed for increasingly high magnifications,more and more zoom lens systems now incorporate a vibration correctionfunction. In this trend, in recent years, even low-magnification zoomlens systems have come to incorporate a vibration correction function.There are also available imaging devices that achieve vibrationcorrection by moving an image sensor on a plane perpendicular to theoptical axis. Thus, a vibration correction function is acquiring thestatus of almost a standard function.

SUMMARY OF THE INVENTION

Against the background discussed above, an object of the presentinvention is to provide a variable-magnification optical system that hasa lightweight focusing group combined with a vibration correctionfunction and that can be made compact in terms of the total opticallength, and to provide an imaging optical device and a digital applianceprovided with such a variable-magnification optical system.

According to one aspect of the present invention, avariable-magnification optical system includes, from the object side, afirst lens group having a positive optical power, a second lens grouphaving a negative optical power, a third lens group having a positiveoptical power, a fourth lens group having a positive optical power, anda fifth lens group having a negative optical power. Thevariable-magnification optical system achieves magnification variationfrom the wide-angle end to the telephoto end by varying all the axialdistances between the lens groups. The variable-magnification opticalsystem achieves focusing by moving the fourth lens group as a focusinggroup in the optical axis direction. The variable-magnification opticalsystem achieves vibration correction by moving all or part of the fifthlens group as a vibration correction group in a direction perpendicularto the optical axis. Moreover, Formulae (1) to (3) below are fulfilled:4.0<|f1/f2<6.0  (1)1.0<f4/f1<1.5  (2)2.0<|f4/fv|<4.0  (3)

where

f1 represents the focal length of the first lens group;

f2 represents the focal length of the second lens group;

f4 represents the focal length of the fourth lens group; and

fv represents the focal length of the vibration correction group.

According to another aspect of the present invention, avariable-magnification optical system includes, from the object side, afirst lens group having a positive optical power, a second lens grouphaving a negative optical power, a third lens group having a positiveoptical power, a fourth lens group having a positive optical power, anda fifth lens group having a negative optical power. Thevariable-magnification optical system achieves magnification variationby varying axial distances between the lens groups. Thevariable-magnification optical system achieves focusing by moving thefourth lens group along the optical axis. The variable-magnificationoptical system achieves vibration correction by moving a sub groupincluding the most image-side lens element within the second lens groupon a plane perpendicular to the optical axis. Moreover, Formula (7)below is fulfilled:M/N<0.5  (7)

where

-   -   M represents a number of lens elements composing the sub group;        and    -   N represents a number of lens elements composing the second lens        group, lens elements constituting a doublet lens element being        counted individually.

According to yet another aspect of the present invention, an imagingoptical device includes a variable-magnification optical system asdescribed above and an image sensing device for converting an opticalimage formed on its light-receiving surface into an electrical signal,and the variable-magnification optical system is arranged such that anoptical image of a subject is formed on the light-receiving surface ofthe image sensing device.

According to still another aspect of the present invention, a digitalappliance includes an imaging optical device as described above so as toadditionally have at least one of a function of taking a still image ofa subject and a function of taking a moving image of a subject.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 comprises optical construction diagrams of a first embodiment(Example 1) of the present invention;

FIG. 2 comprises optical construction diagrams of a second embodiment(Example 2) of the present invention;

FIG. 3 comprises optical construction diagrams of a third embodiment(Example 3) of the present invention;

FIG. 4 comprises optical construction diagrams of a fourth embodiment(Example 4) of the present invention;

FIGS. 5A to 5I are longitudinal aberration diagrams of Example 1;

FIGS. 6A to 6I are longitudinal aberration diagrams of Example 2;

FIGS. 7A to 7I are longitudinal aberration diagrams of Example 3;

FIGS. 8A to 8I are longitudinal aberration diagrams of Example 4;

FIGS. 9A to 9F are lateral aberration diagram of Example 1, at thewide-angle end;

FIGS. 10A to 10F are lateral aberration diagram of Example 1, at themiddle focal length;

FIGS. 11A to 11F are lateral aberration diagram of Example 1, at thetelephoto end;

FIGS. 12A to 12F are lateral aberration diagram of Example 2, at thewide-angle end;

FIGS. 13A to 13F are lateral aberration diagram of Example 2, at themiddle focal length;

FIGS. 14A to 14F are lateral aberration diagram of Example 2, at thetelephoto end;

FIGS. 15A to 15F are lateral aberration diagram of Example 3, at thewide-angle end;

FIGS. 16A to 16F are lateral aberration diagram of Example 3, at themiddle focal length;

FIGS. 17A to 17F are lateral aberration diagram of Example 3, at thetelephoto end;

FIGS. 18A to 18F are lateral aberration diagram of Example 4, at thewide-angle end;

FIGS. 19A to 19F are lateral aberration diagram of Example 4, at themiddle focal length;

FIGS. 20A to 20F are lateral aberration diagram of Example 4, at thetelephoto end;

FIG. 21 comprises optical construction diagrams of a fifth embodiment(Example 5) of the present invention;

FIG. 22 comprises optical construction diagrams of a sixth embodiment(Example 6) of the present invention;

FIG. 23 comprises optical construction diagrams of a seventh embodiment(Example 7) of the present invention;

FIGS. 24A to 24I are longitudinal aberration diagrams of Example 5;

FIGS. 25A to 25I are longitudinal aberration diagrams of Example 6;

FIGS. 26A to 26I are longitudinal aberration diagrams of Example 7;

FIGS. 27A to 27E are lateral aberration diagram of Example 5, withoutand with camera shake correction, at the wide-angle end;

FIGS. 28A to 28E are lateral aberration diagram of Example 5, withoutand with camera shake correction, at the telephoto end;

FIGS. 29A to 29E are lateral aberration diagram of Example 6, withoutand with camera shake correction, at the wide-angle end;

FIGS. 30A to 30E are lateral aberration diagram of Example 6, withoutand with camera shake correction, at the telephoto end;

FIGS. 31A to 31E are lateral aberration diagram of Example 7, withoutand with camera shake correction, at the wide-angle end;

FIGS. 32A to 32E are lateral aberration diagram of Example 7, withoutand with camera shake correction, at the telephoto end;

FIG. 33 is a schematic diagram showing an example of an outlineconfiguration of a digital appliance incorporating avariable-magnification optical system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, variable-magnification optical systems of a first and asecond type, imaging optical devices, and digital appliances accordingto the present invention will be described. A variable-magnificationoptical system of the first type is a variable-magnification opticalsystem that includes, from the object side, a first lens group having apositive optical power, a second lens group having a negative opticalpower, a third lens group having a positive optical power, a fourth lensgroup having a positive optical power, and a fifth lens group having anegative optical power (an optical power is a quantity defined as thereciprocal of a focal length) and that achieves magnification variationfrom the wide-angle end to the telephoto end by varying all the axialdistances between the lens groups. Moreover, it achieves focusing bymoving the fourth lens group as a focusing group in the optical axisdirection, and achieves vibration correction (that is, camera shakecorrection) by moving all or part of the fifth lens group as a vibrationcorrection group in a direction perpendicular to the optical axis.

By adopting a construction including apositive-negative-positive-positive power arrangement from the objectside as described above, it is possible to cover the larger part of theburden for magnification variation with variation in the group-to-groupdistances between the first and second lens groups and between thesecond and third lens groups, and this is advantageous from theviewpoint of total optical length. By achieving focusing with the fourthlens group, it is possible to separate the lens group for focusing fromthe lens group for magnification variation, and this makes it possibleto achieve satisfactory focusing in any magnification variation state.By arranging a vibration correction group in the fifth lens group, it ispossible to achieve vibration correction rearward of the fourth lensgroup which is the focusing group, and this makes it possible to reducedifferences in incidence positions of off-axial rays entering thevibration correction group in any focusing state from infinity toclose-up. It is thus possible to achieve satisfactory vibrationcorrection.

In the above construction, to obtain high performance, it is preferablethat Formulae (1) to (3) below be fulfilled.4.0<|f1/f2|<6.0  (1)1.0<f4/f1<1.5  (2)2.0<|f4/fv|<4.0  (3)

where

f1 represents the focal length of the first lens group;

f2 represents the focal length of the second lens group;

f4 represents the focal length of the fourth lens group; and

fv represents the focal length of the vibration correction group.

Formula (1) defines the focal length ratio between the first and secondlens groups. Below the lower limit of Formula (1), the optical power ofthe first lens group is excessively high, and thus the burden formagnification variation between the first and second lens groups isheavy, resulting in increased coma aberration in the negative direction.Above the upper limit of Formula (1), the optical power of the secondlens group is excessively high, and thus the burden for magnificationvariation between the second and third lens groups is heavy, resultingin increased coma aberration in the positive direction. Thus, fulfillingFormula (1) helps achieve high performance during magnificationvariation with a good balance.

Formula (2) defines the focal length ratio between the fourth and firstlens groups. Below the lower limit of Formula (2), the optical power ofthe fourth lens group is excessively high, resulting in notablevariation in astigmatism and coma aberration during focusing. Above theupper limit of Formula (2), the optical power of the fourth lens groupis excessively low, and this increases the amount of movement of thefourth lens group during focusing (in particular, at the telephoto end),resulting in increased variation in axial chromatic aberration andspherical aberration. Thus, fulfilling Formula (2) helps achieve highperformance during focusing with a good balance.

Formula (3) defines the focal length ratio between the vibrationcorrection group and the fourth lens group. Below the lower limit ofFormula (3), the optical power of the vibration correction group isexcessively low, and this increases the amount of decentering of thevibration correction group needed for vibration correction, resulting inincreased variation in lateral chromatic aberration. Above the upperlimit of Formula (3), the optical power of the vibration correctiongroup is excessively high, resulting in increased variation in comaaberration during vibration correction. Thus, fulfilling Formula (3)helps achieve high performance during vibration correction with a goodbalance.

With the distinctive construction described above, it is possible toobtain a variable-magnification optical system and an imaging opticaldevice that has a lightweight focusing group combined with a vibrationcorrection function and that can be made compact in terms of opticaltotal length. By employing such a variable-magnification optical systemor an imaging optical device that is compact and has a vibrationcorrection function in digital appliances such as digital cameras, it ispossible to add a high performance image input function to the digitalappliances in a compact fashion, and this contributes to achievingcompactness, low cost, high performance, high functionality, etc. in thedigital appliances. For example, a variable-magnification optical systemof the first type is suitable as an interchangeable lens for mirrorlessinterchangeable-lens digital cameras, and, with it, it is possible toobtain a compact, lightweight interchangeable lens convenient to carry.Conditions for obtaining those benefits with a good balance, and forachieving higher optical performance, further compactness, etc., will bedescribed below.

It is preferable that Formula (4) below be fulfilled.2.5<f4/f3<4.5  (4)

where

f3 represents the focal length of the third lens group; and

f4 represents the focal length of the fourth lens group.

Formula (4) defines the focal length ratio between the third and fourthlens groups. Below the lower limit of Formula (4), the optical power ofthe third lens group is excessively low, and this reduces the burden formagnification variation between the second and third lens groups andhence increases the burden for magnification variation on the fourthlens group, making it impossible to obtain satisfactory performance overthe entire focusing range. Above the upper limit of Formula (4), theoptical power of the third lens group is excessively high, and thisincreases the burden for magnification variation between the second andthird lens groups, resulting in large variation in coma aberration.Thus, fulfilling Formula (4) helps obtain high performance duringmagnification variation and during focusing with a good balance.

It is preferable that an aperture stop be arranged between the secondand third lens groups. By arranging an aperture stop between the secondand third lens groups, it is possible to correct the astigmatism andcoma aberration occurring in the second lens group with the third andfollowing lens groups, and this helps correct astigmatism and comaaberration satisfactorily over the entire magnification variation range.It is therefore preferable to set the position of an aperture stopbetween the second and third lens groups in the variable-magnificationoptical system.

It is preferable that the vibration correction group be composed of asingle lens element or a doublet lens element made up of a negative lenselement and a positive lens element. By limiting the number of lenselements composing the vibration correction group in this way, it ispossible to suppress the weight of the vibration correction group, andthus to reduce the members and the like necessary to drive the vibrationcorrection group. This is advantageous to size reduction of the opticalsystem.

It is preferable that Formula (5) below be fulfilled.0.1<(R5A+R5B)/(R5A−R5B)<0.70  (5)

where

-   -   R5A represents the radius of curvature of the surface arranged        at the most object-side position in the vibration correction        group; and    -   R5B represents the radius of curvature of a surface concave to        the image side in the vibration correction group.

It is preferable that the most object-side surface in the vibrationcorrection group is concave to the object side. It is also preferablethat the vibration correction group have at least one lens surfaceconcave to the image-surface side. With this construction, it ispossible to suppress variation in coma aberration during vibrationcorrection, and to obtain satisfactory vibration correction performance.A lens surface shape in the vibration correction group is specificallydefined by Formula (5). Outside the range defined by Formula (5), it isdifficult to suppress variation in coma aberration during vibrationcorrection, resulting in notable degradation in performance duringvibration correction. For example, below the lower limit of Formula (5),coma aberration varies greatly in the positive direction duringvibration correction; above the upper limit of Formula (5), comaaberration varies greatly in the negative direction during vibrationcorrection. Thus, fulfilling Formula (5) helps achieve high performanceduring vibration correction with a good balance.

It is preferable that the focusing group be composed of a single lenselement or a doublet lens element made up of a negative lens element anda positive lens element. By limiting the number of lens elementscomposing the focusing group in this way, it is possible to reduce theweight of the focusing group, and to obtain a construction suitable forcontrast AF.

It is preferable that Formula (6) below be fulfilled.1.0<(R4A+R4B)/(R4A−R4B)<1.2  (6)

where

-   -   R4A represents the radius of curvature of the most object-side        surface in the fourth lens group; and    -   R4B represents the radius of curvature of the most image-side        surface in the fourth lens group.

It is preferable that the fourth lens group, which is the focusinggroup, include a meniscus shape concave to the object side. By using apositive meniscus lens element concave to the object side in thefocusing group, it is possible to suppress variation in coma aberrationand astigmatism during focusing. A lens surface shape in the focusinggroup is specifically defined by Formula (6). Above the upper limit ofFormula (6), the optical power of the focusing group is excessively low,and this increases the amount of movement of the focusing group duringfocusing, in particular in a telephoto state, resulting in largevariation in axial chromatic aberration and spherical aberration duringfocusing. Below the lower limit of Formula (6), the optical power of theimage-side surface of the focusing group is so high as to causeincidence positions of off-axial rays to vary with focusing, resultingin large variation in astigmatism and coma aberration. Thus, fulfillingFormula (6) helps achieve high performance during focusing with a goodbalance.

A variable-magnification optical system of the second type is avariable-magnification optical system that includes, from the objectside, a first lens group having a positive optical power, a second lensgroup having a negative optical power, a third lens group having apositive optical power, a fourth lens group having a positive opticalpower, and a fifth lens group having a negative optical power (anoptical power is a quantity defined as the reciprocal of a focal length)and that achieves magnification variation by varying axial distancesbetween the lens groups. Moreover, it achieves focusing by moving thefourth lens group along the optical axis, and achieves vibrationcorrection by moving a sub group including the most image-side lenselement in the second lens group on a plane substantially perpendicularto the optical axis.

In a power arrangement that includes five lens groups, namely apositive, a negative. a positive, a positive, and a negative lens groupfrom the object side as described above, when a vibration correctionlens group is arranged within the second lens group, a drive mechanismfor driving the fourth lens group, which is the focusing group, and adrive mechanism for driving the sub group, which is the vibrationcorrection lens group, are located far away from each other, offeringthe advantage of higher layout efficiency inside a lens barrel. Theentire second lens group may instead be used as the vibration correctionlens group. In that case, however, since the second lens group has acomparatively large lens diameter and hence is comparatively heavy, todrive it at a sufficient speed to cope with the frequencies of camerashake, it is necessary to use a drive mechanism that produces a powerfuldriving force. This leads to an increased size of the system as a whole.

In a variable-magnification optical system that includes five lensgroups, namely a positive, a negative, a positive, a positive, and anegative lens group from the object side, magnification variation actionascribable to variation in the distances between the first and secondlens groups and between the second and third lens groups accounts forthe large part of the magnification variation action of the entireoptical system. Accordingly, to make the variable-magnification opticalsystem compact, it is effective to increase the optical power of thesecond lens group. To achieve that, a negative lens element having acomparatively high optical power needs to be arranged within the secondlens group, but if this lens element is decentered for vibrationcorrection, large eccentric aberration occurs, and this makes itdifficult to secure satisfactory performance during vibrationcorrection. In general, when a plurality of lens groups are in arelationship where they produce aberrations of opposite signs to canceleach other's aberrations (that is, in a relationship of a strong bond interms of aberrations), decentering one of them produces large eccentricaberration.

From the above viewpoint, in a case where part of a lens group is usedas a vibration correction lens group, it is not advisable to drive a sublens group located in the middle of the lens group for vibrationcorrection, with the lens group divided into three groups, namely astationary group, a vibration correction group, and a stationary group.It is more advantageous to drive an outer sub lens group abutting agroup-to-group distance, with the lens group divided into two groups,namely a vibration correction group and a stationary group. This helpsachieve greater independence among the sub lens groups in terms ofaberrations without increasing the number of lens elements.

In a variable-magnification optical system that includes five lensgroups, namely a positive, a negative. a positive, a positive, and anegative lens group from the object side, to allow passage of off-axialrays at the wide-angle end, the most object-side lens element in thesecond lens group has a comparatively large lens diameter. Accordingly,it is preferable to use, not the object-side sub lens group within thesecond lens group, but the image-side sub lens group within the secondlens group as the vibration correction lens group, from the viewpoint ofweight. Moreover, inside the second lens group, outside an image-sidelens element in the radial direction, a space is left due to thedifference between the diameters of object-side and image-side lenselements, and a drive mechanism for vibration correction can be arrangedthere, which is another advantage from the viewpoint of spaceefficiency.

In addition, to reduce the weight of the vibration correction lensgroup, it is preferable that Formula (7) below be fulfilled.M/N<0.5  (7)

where

-   -   M represents the number of lens elements composing the sub        group; and    -   N represents the number of lens elements composing the second        lens group, lens elements constituting a doublet lens element        being counted individually.

If the number M of lens elements composing the sub group is so large asto fall outside the range given by Formula (7), the increased weight ofthe vibration correction lens group requires an increased driving forceand hence a larger actuator, resulting in an increased size of thesystem as a whole. The second lens group has the highest optical powerin the variable-magnification optical system, and thus the number N oflens elements composing the second lens group greatly affects the sizeof the system as a whole. Accordingly, if the number N of lens elementscomposing the second lens group is so small as to fall outside the rangegiven by Formula (7), retaining a high optical power makes correction ofaberrations (in particular, astigmatism) difficult, and compromisingwith a lower optical power leads to an increased size of the system as awhole. Thus, fulfilling Formula (7) helps achieve compactness, highperformance, etc. with a good balance in the variable-magnificationoptical system having a vibration correction function.

With the distinctive construction described above, it is possible toachieve a high-performance variable-magnification optical system and ahigh-performance imaging optical device that have a lightweight focusinggroup, that is compact in terms of the size of the optical system as awhole, and that nevertheless offers a vibration correction function. Byemploying such a variable-magnification optical system or an imagingoptical device that is compact and has a vibration correction functionin digital appliances such as digital cameras, it is possible to add ahigh performance image input function to the digital appliances in acompact fashion, and this contributes to achieving compactness, lowcost, high performance, high functionality, etc. in the digitalappliances. For example, a variable-magnification optical system of thesecond type is suitable as an interchangeable lens for mirrorlessinterchangeable-lens digital cameras, and, with it, it is possible torealize a compact, lightweight interchangeable lens convenient to carry.Conditions for obtaining those benefits with a good balance, and forachieving higher optical performance, further compactness, etc., will bedescribed below.

It is preferable that Formula (8) below be fulfilled.3.0<fv/f2<12.0  (8)

where

fv represents the focal length of the sub group; and

f2 represents the focal length of the second lens group.

Below the lower limit of Formula (8), the optical power of the vibrationcorrection lens group is excessively high, and this makes it difficultto suppress the aberrations produced by the vibration correction lensgroup itself. This leads to, for example, increased spherical aberrationand astigmatism. Increased spherical aberration causes increasedeccentric coma aberration to occur during decentering for vibrationcorrection. Increased astigmatism causes increased inclination of theimage surface (so-called one-sided blur) to occur during decentering forvibration correction. By contrast, above the upper limit of Formula (8),the optical power of the vibration correction lens group is excessivelylow, and this either makes it difficult to secure the desired vibrationcorrection sensitivity, or makes it necessary to increase the movementdistance of the vibration correction lens group, resulting in anincreased size of the variable-magnification optical system. Also, anincreased optical power of the second lens group as a whole may causeincreased variation in astigmatism during zooming. Thus, fulfillingFormula (8) helps achieve compactness, high performance, etc. with agood balance in the variable-magnification optical system having avibration correction function.

It is further preferable that Formula (8a) below be fulfilled.4.0<fv/f2<10.0  (8a)Formula (8a) defines a further preferable conditional range within theconditional range defined by Formula (8) above from the above-mentionedviewpoints. Accordingly, preferably, fulfilling Formula (8a) helpsobtain the above-mentioned benefits more effectively.

It is preferable that Formula (9) below be fulfilled.−4.0<(rA+rB)/(rA−rB)<−0.7  (9)

where

-   -   rA represents the radius of curvature of the most object-side        surface in the sub group; and    -   rB represents the radius of curvature of the most image-side        surface in the sub group.

Arranging the negative lens element having the highest optical powerwithin the second lens group at the most object-side position in thesecond lens group is effective in reducing the lens diameter of thesecond lens group. In that case, a convergent beam having passed throughthe first lens group having a positive optical power is turned into adivergent bean by the negative lens element having the high negativeoptical power arranged at the most object-side position in the secondlens group, and then travels on toward the image side with graduallyincreasing ray heights within the second lens group. Above the upperlimit of Formula (9), the front and rear surfaces of the vibrationcorrection lens group (that is, the sub group) produce large sphericalaberration, and this make it difficult to reduce the sphericalaberration produced by the vibration correction lens group itself. As aresult, decentering the vibration correction lens group producesincreased eccentric coma aberration, and this makes it difficult tosecure satisfactory optical performance during vibration correction. Bycontrast, below the lower limit of Formula (9), while the sphericalaberration produced by the vibration correction lens group itself canadvantageously be suppressed, it is difficult to secure the opticalpower desired in the vibration correction lens group itself. Thus,fulfilling Formula (9) helps achieve compactness, high performance, etc.with a good balance in the variable-magnification optical system havinga vibration correction function.

It is further preferable that Formula (9a) below be fulfilled.−3.0<(rA+rB)/(rA−rB)<−0.9  (9a)Formula (9a) defines a further preferable conditional range within theconditional range defined by Formula (9) above from the above-mentionedviewpoints. Accordingly, preferably, fulfilling Formula (9a) helpsobtain the above-mentioned benefits more effectively.

It is preferable that, within the second lens group, an asphericalsurface be arranged to the object side of the sub group. In a case wherethe aberrations produced by the vibration correction lens group itselfwithin the second lens group are sufficiently suppressed, theaberrations produced by the other lens group there, namely thestationary group (that is, the part of the second lens group on theobject side of the sub group), also need to be sufficiently suppressed.Otherwise, the second lens group as a whole produces large aberrationsafter all, and this makes it difficult to suppress variation inperformance during zooming. As described previously, to make thevariable-magnification optical system compact, it is necessary toincrease the optical power of the second lens group. Thus, an increasein the number of lens elements within the second lens group caneffectively be avoided by arranging an aspherical surface in thestationary group.

It is preferable that, within the second lens group, a positive lenselement having a biconvex shape be arranged so as to cancel theaberrations produced by the negative lens element having the highnegative optical power. It is also preferable that the above-mentionedaspherical surface be arranged only on the positive lens element havingthe biconvex shape from the viewpoint of the moldability of theaspherical-surface lens, that is, from the viewpoint of cost.Accordingly, it is preferable that the above-mentioned lens elementincluding the aspherical surface be a single biconvex positive lenselement.

It is preferable that the sub group be composed of a single negativelens element, and that Formula (10) below be fulfilled.ft/Ymax<7.5  (10)

where

-   -   ft represents the focal length of the entire system at the        telephoto end; and    -   Ymax represents the maximum image height in terms of an ideal        image height excluding distortion, being a quantity fulfilling        the relationship ω=tan⁻¹ (Ymax/f), where f represents the focal        length of the entire system and to represents the half-angle of        view.

It is preferable that the vibration correction lens group be composed ofa single negative lens element, because that helps achieve weightreduction for reducing the load to be driven for vibration correction.Here, above the upper limit of Formula (10), the lateral chromaticaberration occurring during decentering of the vibration correction lensgroup is excessively large as compared with the maximum image height,and this makes it difficult to secure satisfactory optical performanceduring vibration correction.

It is preferable that Formula (11) below be fulfilled.60<Vd  (11)

where

-   -   Vd represents the Abbe number of the negative lens element        composing the sub group.

In a case where the vibration correction lens group is composed of asingle negative lens element, it is preferable that Formula (11) befulfilled. Below the lower limit of Formula (11), increased lateralchromatic aberration occurs during vibration correction, and this makesit difficult to secure satisfactory optical performance during vibrationcorrection.

It is preferable that the sub group be composed of a doublet lenselement made up of a negative lens element and a positive lens element.By using a doublet lens element made up of a negative lens element and apositive lens element as the vibration correction lens group, it ispossible to suppress lateral chromatic aberration occurring duringdecentering of the vibration correction lens group. It is then, ascompared with when discrete lens elements are used, also possible tosuppress degraded aberrations resulting from an error in the positionsof the negative and positive lens elements relative to each otheroccurring during manufacture.

It is preferable that the third and fifth lens groups move togetherduring magnification variation. In a construction where the third andfifth lens groups move together during magnification variation, thethird and fifth lens groups can be mounted on a single moving mechanism.Thus, with this construction, it is possible to reduce factors leadingto manufacturing errors, and to alleviate degradation in performanceresulting from manufacturing errors.

It is preferable that the third lens group, the driving mechanism formoving the fourth lens group for focusing, and the fifth lens group movetougher, and it is further preferable that the driving mechanism varythe axial distance between the third and fourth lens groups and theaxial distance between the fourth and fifth lens groups. In aconstruction where the third lens group, the fourth lens group drivingmechanism, and the fifth lens group move together, the third lens group,the fourth lens group driving mechanism, and the fifth lens group can bemounted on a single moving group. With this construction, in a lenssystem designed to be capable of purely mechanical zooming, that is,so-called manual zooming, depending on the focus state, an abruptmagnification variation operation by a user may cause collision betweenthe focusing group and a neighboring lens group. Accordingly, measuresneed to be provided to protect the lens system from destruction in theevent of collision. On the other hand, with a construction where thethird lens group, the fourth lens group driving mechanism, and the fifthlens group are mounted on a single moving group as described above,irrespective of the focus state, it is possible to perfectly ensure thatno collision occurs between the fourth lens group with the third lensgroup or the fifth lens group. It is thus no longer necessary to providemeasures as mentioned above, and this helps simplify the mechanism.

It is preferable that Formula (12) below be fulfilled.−4.0<f5/f3<−0.8  (12)

where

f3 represents the focal length of the third lens group; and

f5 represents the focal length of the fifth lens group.

Below the lower limit of Formula (12), the optical power of the fifthlens group is extremely low relative to that of the third lens group,and thus the magnification variation action exerted by movement of thefifth lens group is insufficient. By contrast, above the upper limit ofFormula (12), the optical power of the fifth lens group is excessivelyhigh relative to that of the third lens group, and this makes itdifficult to locate the rear principal point close to the image surfaceat the wide-angle end, and thus to obtain the desired focal length atthe wide-angle end. Whether insufficient magnification variation actionor difficulty securing the desired focal length at the wide-angle end,the consequence is difficulty with aberration correction and the like inthe variable-magnification optical system as a whole, leaving largeaberrations uncorrected on the whole, hence resulting in degradedoptical performance. Thus, fulfilling Formula (12) helps achievecompactness, high performance, etc. with a good balance in thevariable-magnification optical system having a vibration correctionfunction.

It is further preferable that Formula (12a) below be fulfilled.−2.0<f5/f3<−1.0  (12a)Formula (12a) defines a further preferable conditional range within theconditional range defined by Formula (12) above from the above-mentionedviewpoints. Accordingly, preferably, fulfilling Formula (12a) helpsobtain the above-mentioned benefits more effectively.

It is preferable that Formula (13) below be fulfilled.−1.0<M5/f5<−0.1  (13)

where

-   -   M5 represents the distance along the optical axis from the        position of the fifth lens group at the wide-angle end and the        position of the fifth lens group at the telephoto end; and    -   f5 represents the focal length of the fifth lens group.

Below the lower limit of Formula (13), either the optical power of thefifth lens group is excessively high, or the amount of movement of thefifth lens group is excessively large, and this makes it difficult tosuppress variation in astigmatism and coma aberration that accompaniesthe movement of the fifth lens group. By contrast, above the upper limitof Formula (13), either the amount of movement of the fifth lens groupis excessively small, or the optical power of the fifth lens group isexcessively low, and thus the magnification variation action by thefifth lens group is insufficient. As a result, to obtain the desiredmagnification variation, it is then necessary to increase themagnification variation action between the first and second lens groups.This leads to either an increased total length of the optical system atthe telephoto end, or, as a consequence of avoiding that, an increasedoptical power in the second lens group, this in turn making it difficultto suppress variation in astigmatism and coma aberration duringmagnification variation. Thus, fulfilling Formula (13) helps achievecompactness, high performance, etc. with a good balance in thevariable-magnification optical system having a vibration correctionfunction.

It is further preferable that Formula (13a) below be fulfilled.−0.7<M5/f5<−0.2  (13a)Formula (13a) defines a further preferable conditional range within theconditional range defined by Formula (13) above from the above-mentionedviewpoints. Accordingly, preferably, fulfilling Formula (13a) helpsobtain the above-mentioned benefits more effectively.

It is preferable that Formula (14) below be fulfilled.1.0<f4/f3<4.0  (14)

where

f3 represents the focal length of the third lens group; and

f4 represents the focal length of the fourth lens group.

Below the lower limit of Formula (14), the optical power of the fourthlens group relative to that of the third lens group is excessively high,and this makes it difficult to suppress variation in astigmatism thataccompanies the movement of the fourth lens group during focusing. Bycontrast, above the upper limit of Formula (14), the larger part of theconverging action of the optical system concentrates on the third lensgroup, and thus the third lens group produces increased sphericalaberration and coma aberration. Thus, fulfilling Formula (14) helpsachieve a compactness, high performance, etc. with a good balance in thevariable-magnification optical system having a vibration correctionfunction.

It is further preferable that Formula (14a) below be fulfilled.1.1<f4/f3<3.0  (14a)Formula (14a) defines a further preferable conditional range within theconditional range defined by Formula (14) above from the above-mentionedviewpoints. Accordingly, preferably, fulfilling Formula (14a) helpsobtain the above-mentioned benefits more effectively.

It is preferable that Formula (15) below be fulfilled.0.5<M4/M5<1.5  (15)

where

-   -   M4 represents the distance along the optical axis from the        position of the fourth lens group at the wide-angle end to the        position of the fourth lens group at the telephoto end; and    -   M5 represents the distance along the optical axis from the        position of the fifth lens group at the wide-angle end to the        position of the fifth lens group at the telephoto end.

Below the lower limit of Formula (15), the amount of movement of thefourth lens group is excessively small relative to that of the fifthlens group, and it is then necessary, to secure the movement amount ofthe fifth lens group necessary to obtain the desired magnificationvariation, to secure a large distance between the fourth and fifth lensgroups at the wide-angle end. As a result, the rear principal point ofthe entire optical system is located away from the image surface, andthis makes it difficult to obtain the desired focal length at thewide-angle end. By contrast, below the upper limit of Formula (15), theamount of movement of the fourth lens group is excessively largerelative to that of the fifth lens group, and it is then necessary, tosecure the desired amount of movement for focusing, to secure a largedistance between the third and fifth lens groups at the wide-angle end.As a result, the optical system has an increased size. Or, to avoidthat, it is necessary to increase the optical power of the fourth lensgroup, and this makes it difficult to suppress variation in astigmatismthat accompanies the movement of the fourth lens group during focusing.Thus, fulfilling Formula (15) helps achieve compactness, highperformance, etc. with a good balance in the variable-magnificationoptical system having a vibration correction function.

It is further preferable that Formula (15a) below be fulfilled.0.6<M4/M5<1.2  (15a)Formula (15a) defines a further preferable conditional range within theconditional range defined by Formula (15) above from the above-mentionedviewpoints. Accordingly, preferably, fulfilling Formula (15a) helpsobtain the above-mentioned benefits more effectively.

Variable-magnification optical systems of the first and second types aresuitable for use as imaging lenses in digital appliances having an imageinput function (for example, digital cameras); by combining one with animage sensing device or the like, it is possible to build an imagingoptical device that takes in an image of an object optically and outputsit in the form of an electric signal. An imaging optical device is anoptical device that constitutes a main component of a camera used totake a still and a moving picture of a subject, and is composed of, fromthe object side (that is, the subject side), a variable-magnificationoptical system (for example, a zoom lens system) for forming an opticalimage of an object and an image sensing device for converting theoptical image formed by the variable-magnification optical system intoan electrical signal. By arranging a variable-magnification opticalsystem having one of the distinctive constructions described previouslysuch that an optical image of a subject is formed on a light-receivingsurface (that is, an imaging surface) of the image sensing device, it ispossible to build a compact, inexpensive, high-performance imagingoptical device, and a digital appliance provided with it.

Examples of digital appliances having an image input function includecameras such as digital cameras, video cameras, surveillance cameras,vehicle-mounted cameras, and cameras for videophones. Also included areany digital appliances and the like having a camera function added tothem by incorporation or by optional attachment, such as personalcomputers, portable digital appliances (for example, cellular phones,smart phones (multifunction cellular phones), and mobile computers), andperipheral devices for them (for example, scanners and printers). Asthese examples suggest, imaging optical devices can not only be used tobuild cameras, but also be combined with various appliances to add acamera function to them. For example, it is possible to build digitalappliances having an image input function, such as camera-equippedcellular phones.

FIG. 33 shows an example of an outline configuration of a digitalappliance DU as one example of a digital appliance having an image inputfunction, in a schematic cross section. The imaging optical device LUincorporated in the digital appliance DU shown in FIG. 33 includes, fromthe object side (that is, the subject side), a zoom lens system ZL (withan optical axis AX) which forms an optical image (image surface) IM ofan object at varying magnifications, a plane-parallel plate PT(corresponding to a cover glass of an image sensing device SR, andoptical filters and the like arranged as necessary, such as an opticallow-pass filter and an infrared-cut filter), and an image sensing deviceSR which converts into an electrical signal the optical image IM formedon the light-receiving surface (imaging surface) SS by the zoom lenssystem ZL. When a digital appliance DU having an image input function isbuilt with this imaging optical device LU, typically, the imagingoptical device LU is arranged inside the body of the digital applianceDU. For the purpose of realizing a camera function, it is possible toadopt a configuration that suits specific requirements. For example, animaging optical device LU built as a unit can be designed to bedetachably attached to, or rotatably fitted to, the body of a digitalappliance DU.

A zoom lens system ZL as a variable-magnification optical system of thefirst type is a variable-magnification optical system that has five lensgroups, namely a positive, a negative, a positive, a positive, and anegative lens group, and that achieves magnification variation (that is,zooming) from the wide-angle end to the telephoto end by varying all theaxial distances between the lens groups. It achieves focusing by movingthe fourth lens group as a focusing group in the optical axis AXdirection, and achieves vibration correction by moving all or part ofthe fifth lens group as a vibration correction group in a directionperpendicular to the optical axis AX.

A zoom lens system ZL as a variable-magnification optical system of thesecond type is a variable-magnification optical system that has fivelens groups, namely a positive, a negative, a positive, a positive, anda negative lens group, and that achieves magnification variation (thatis, zooming) by varying axial distances between the lens groups. Itachieves focusing by moving the fourth lens group along the optical axisAX, and achieves vibration correction by moving a sub group includingthe most image-side lens element in the second lens group on a planesubstantially perpendicular to the optical axis AX. During magnificationvariation, at least the third, fourth, and fifth lens groups moverelative to the image surface, and an optical image IM is formed on thelight-receiving surface SS of the image sensing device SR.

Used as the image sensing device SR is, for example, a solid-state imagesensor, such as a CCD (charge-coupled device) image sensor or a CMOS(complementary metal-oxide semiconductor) image sensor, having aplurality of pixels. The zoom lens system ZL is so arranged that theoptical image IM of the subject is formed on the light-receiving surfaceSS, which is the photoelectric conversion portion of the image sensingdevice SR. Thus, the optical image IM formed by the zoom lens system ZLis converted into an electrical signal by the image sensing device SR.

The digital appliance DU includes, in addition to the imaging opticaldevice LU, a signal processor 1, a controller 2, a memory 3, anoperation panel 4, a display 5, etc. The signal generated by the imagesensing device SR is subjected to predetermined digital imageprocessing, image compression, etc. as necessary in the signal processor1, and is recorded, as a digital video signal, to the memory 3 (asemiconductor memory, an optical disk, or the like) or, as the case maybe, transferred to an external device via a cable or after beingconverted into an infrared signal (for example, a communication functionof a cellular phone). The controller 2 comprises a microprocessor, andcontrols, in a centralized fashion, image taking functions (such as astill image taking function and a moving image taking function),functions such as an image playback function, and operation of lensmovement mechanisms for zooming, focusing, camera shake correct, etc.For example, the controller 2 controls the imaging optical device LU toperform at least either shooting of a still image of a subject orshooting of a moving image of a subject. The display 5 includes adisplay device such as a liquid crystal monitor, and displays an imagebased on an image signal resulting from conversion by the image sensingdevice SR or image information recorded in the memory 3. The operationpanel 4 includes operated members such as operation buttons (forexample, a shutter-release button), operation dials (for example, ashooting mode dial), etc., and conveys information entered by a user tothe controller 2.

Now, by way of a first to a fourth embodiment, specific opticalconstructions of the zoom lens system ZL will be described in moredetail. FIGS. 1 to 4 comprise optical construction diagramscorresponding to the zoom lens system ZL in the first to fourthembodiments respectively, showing, in an optical section, the lensarrangement, lens shapes, etc. observed at the wide-angle end (W), atthe middle focal length (M), and at the telephoto end (T). In the firstto fourth embodiments (FIGS. 1 to 4), the zoom lens system ZL includes,from the object side, a first lens group Gr1 having a positive opticalpower, a second lens group Gr2 having a negative optical power, a thirdlens group Gr3 having a positive optical power, a fourth lens group Gr4having a positive optical power, and a fifth lens group Gr5 having anegative optical power, and is so constructed as to achievemagnification variation (that is, zooming) from the wide-angle end (W)to the telephoto end (T) by varying all the axial distances between thelens groups.

For magnification variation, the first lens group Gr1, the second lensgroup Gr2, the third lens group Gr3, the fourth lens group Gr4, and thefifth lens group Gr5 each move relative to the image surface IM. Anaperture stop ST is located to the object side of the third lens groupGr3, and moves together with the third lens group Gr3 during zooming.For focusing, the fourth lens group Gr4 moves along the optical axis AX.That is, the fourth lens group Gr4 is a focusing group, and as indicatedby arrow mF, moves toward the object side during focusing on a closeobject. The entire fifth lens group Gr5 or a sub group including themost object-side lens element in the fifth lens group Gr5 is a vibrationcorrection group GrV, and as indicated by arrow mV, movesperpendicularly to the optical axis AX for vibration correction.

In the first embodiment (FIG. 1), the zoom lens system ZL has six lensgroups, namely a positive, a negative, a positive, a positive, anegative, and a positive lens group, and has a zoom arrangement where,during zooming, the first to fifth lens groups Gr1 to Gr5 are movableand the sixth lens group Gr6 is stationary. The fourth lens group Gr4acts as a focusing group, and the fifth lens group Gr5 acts as avibration correction group. During zooming from the wide-angle end (W)to the telephoto end (T), the first lens group Gr1 moves monotonicallytoward the object side, the second lens group Gr2 moves monotonicallytoward the image side, the third lens group Gr3 moves monotonicallytoward the object side, the fourth lens group Gr4 first moves toward theobject side and then makes a U-turn toward the image side, and the fifthlens group Gr5 moves monotonically toward the object side.

In the second embodiment (FIG. 2), the zoom lens system ZL has five lensgroups, namely a positive, a negative, a positive, a positive, and anegative lens group, and has a zoom arrangement where, during zooming,the first to fifth lens groups Gr1 to Gr5 are movable. The fourth lensgroup acts as a focusing group, and the most object-side lens elementwithin the fifth lens group Gr5 acts as a vibration correction group.During magnification variation from the wide-angle end (W) to thetelephoto end (T), the first lens group Gr1 moves monotonically towardthe object side, the second lens group Gr2 moves monotonically towardthe image side, the third lens group Gr3 moves monotonically toward theobject side, the fourth lens group Gr4 first moves toward the objectside and then makes a U-turn toward the image side, and the fifth lensgroup Gr5 first moves toward the object side and then makes a U-turntoward the image side.

In the third embodiment (FIG. 3), the zoom lens system ZL has five lensgroups, namely a positive, a negative, a positive, a positive, and anegative lens group, and has a zoom arrangement where, during zooming,the first to fifth lens groups Gr1 to Gr5 are movable. The fourth lensgroup Gr4 acts as a focusing group, and the most object-side doubletlens element within the fifth lens group Gr5 acts as a vibrationcorrection group. During zooming from the wide-angle end (W) to thetelephoto end (T), the first lens group Gr1 moves monotonically towardthe object side, the second lens group Gr2 moves monotonically towardthe image side, the third lens group Gr3 moves monotonically toward theobject side, the fourth lens group Gr4 first moves toward the objectside and then makes a U-turn toward the image side, and the fifth lensgroup Gr5 first moves toward the object side and then makes a U-turntoward the image side.

In the fourth embodiment (FIG. 4), the zoom lens system ZL has five lensgroups, namely a positive, a negative, a positive, a positive, and anegative lens group, and has a zoom arrangement where, during zooming,the first to fifth lens groups Gr1 to Gr5 are movable. The fourth lensgroup Gr4 acts as a focusing group, and the most object-side doubletlens element within the fifth lens group Gr5 acts as a vibrationcorrection group. During zooming from the wide-angle end (W) to thetelephoto end (T), the first lens group Gr1 moves monotonically towardthe object side, the second lens group Gr2 moves monotonically towardthe image side, the third lens group Gr3 moves monotonically toward theobject side, the fourth lens group Gr4 first moves toward the objectside and then makes a U-turn toward the image side, and the fifth lensgroup Gr5 first moves toward the object side and then makes a U-turntoward the image side.

In the first embodiment (FIG. 1), each lens group is composed, in termsof the paraxial surface shapes of the constituent lens elements, asfollows from the object side. The first lens group Gr1 is composed of adoublet lens element made up of a negative meniscus lens element concaveto the image side and a positive meniscus lens element convex to theobject side and a positive meniscus lens element convex to the objectside. The second lens group Gr2 is composed of a negative meniscus lenselement concave to the image side, a biconcave negative lens element, abiconvex positive lens element, and a negative meniscus lens elementconcave to the object side. The third lens group Gr3 is composed of abiconvex positive lens element having aspherical surfaces on both sidesand a doublet lens element made up of a biconcave negative lens elementand a biconvex positive lens element. To the object side of the thirdlens group Gr3, an aperture stop ST is arranged. The fourth lens groupGr4 is composed of a single positive meniscus lens element convex to theimage side and having aspherical surfaces on both sides. The fifth lensgroup Gr5 is composed of a single biconcave negative lens element (avibration correction group GrV). The sixth lens group Gr6 is composed ofa single biconvex positive lens element.

In the second embodiment (FIG. 2), each lens group is composed, in twinsof the paraxial surface shapes of the constituent lens elements, asfollows from the object side. The first lens group Gr1 is composed of adoublet lens element made up of a negative meniscus lens element concaveto the image side and a positive meniscus lens element convex to theobject side and a positive meniscus lens element convex to the objectside. The second lens group Gr2 is composed of two biconcave negativelens elements and a doublet lens element made up of a biconvex positivelens element and a biconcave negative lens element. The third lens groupGr3 is composed of a biconvex positive lens element having asphericalsurfaces on both sides and a doublet lens element made up of a biconcavenegative lens element and a biconvex positive lens element. To theobject side of the third lens group Gr3, an aperture stop ST isarranged. The fourth lens group Gr4 is composed of a single positivemeniscus lens element convex to the image side and having asphericalsurfaces on both sides. The fifth lens group Gr5 is composed of abiconcave negative lens element (a vibration correction group GrV) and abiconvex positive lens element.

In the third embodiment (FIG. 3), each lens group is composed, in termsof the paraxial surface shapes of the constituent lens elements, asfollows from the object side. The first lens group Gr1 is composed of adoublet lens element made up of a negative meniscus lens element concaveto the image side and a positive meniscus lens element convex to theobject side and a positive meniscus lens element convex to the object,side. The second lens group Gr2 is composed of two biconcave negativelens elements and a biconvex positive lens element. The third lens groupGr3 is composed of a biconvex positive lens element having asphericalsurfaces on both sides and a doublet lens element made up of a biconcavenegative lens element and a biconvex positive lens element. To theobject side of the third lens group Gr3, an aperture stop ST isarranged. The fourth lens group Gr4 is composed of a single positivemeniscus lens element convex to the image side and having asphericalsurfaces on both sides. The fifth lens group Gr5 is composed of adoublet lens element (a vibration correction group GrV) made up of abiconcave negative lens element and a positive meniscus lens elementconvex to the object side and a biconvex positive lens element.

In the fourth embodiment (FIG. 4), each lens group is composed, in termsof the paraxial surface shapes of the constituent lens elements, asfollows from the object side. The first lens group Gr1 is composed of adoublet lens element made up of a negative meniscus lens element concaveto the image side and a positive meniscus lens element convex to theobject side and a positive meniscus lens element convex to the objectside. The second lens group Gr2 is composed of two biconcave negativelens elements and a biconvex positive lens element. The third lens groupGr3 is composed of a biconvex positive lens element having asphericalsurfaces on both sides and a doublet lens element made up of a biconcavenegative lens element and a biconvex positive lens element. To theobject side of the third lens group Gr3, an aperture stop ST isarranged. The fourth lens group Gr4 is composed of a doublet lenselement made up of a biconvex positive lens element having an asphericalsurface on the object side and a negative meniscus lens element concaveto the object side and having an aspherical surface on the image side.The fifth lens group Gr5 is composed of a doublet lens element (avibration correction group GrV) made up of a biconcave negative lenselement and a negative meniscus lens element concave to the image sideand a biconvex positive lens element.

Next, by way of a fifth to a seventh embodiment, specific opticalconstructions of the zoom lens system ZL will be described in moredetail. FIGS. 21 to 23 comprise optical construction diagramscorresponding to the zoom lens system ZL in the fifth to seventhembodiments respectively, showing, in an optical section, the lensarrangement, lens shapes, etc. observed at the wide-angle end (W), atthe middle focal length (M), and at the telephoto end (T).

In the fifth to seventh embodiments (FIGS. 21 to 23), the zoom lenssystem ZL includes, from the object side, a first lens group Gr1 havinga positive optical power, a second lens group Gr2 having a negativeoptical power, a third lens group Gr3 having a positive optical power, afourth lens group Gr4 having a positive optical power, and a fifth lensgroup Gr5 having a negative optical power, and is so constructed as toachieve magnification variation (that is, zooming) by varying axialdistances between the lens groups. For magnification variation, at leastthe third lens group Gr3, the fourth lens group Gr4, and the fifth lensgroup Gr5 move relative to the image surface IM. An aperture stop ST islocated at the object side of the third lens group Gr3, and movestogether with the third lens group Gr3 during zooming. For focusing, thefourth lens group Gr4 moves along the optical axis AX. That is, thefourth lens group Gr4 is a focusing group, and as indicated by arrow mF,moves toward the object side during focusing on a close object. A subgroup GrV including the most image-side lens element in the second lensgroup Gr2 is a vibration correction group, and as indicated by arrow mV,moves perpendicularly to the optical axis AX for vibration correction.

In the fifth embodiment (FIG. 21), the zoom lens system ZL has five lensgroups, namely a positive, a negative, a positive, a positive, and anegative lens group, and has a zoom arrangement where, during zooming,all the lens groups are movable. Here, the third lens group Gr3 and thefifth lens group Gr5 are linked together so as to move together. Duringmagnification variation from the wide-angle end (W) to the telephoto end(T), the first lens group Gr1 moves monotonically toward the objectside, the second lens group Gr2 moves first toward the object side andthen toward the image side. The third to fifth lens groups Gr3 to Gr5move monotonically toward the object side.

In the sixth embodiment (FIG. 22), the zoom lens system ZL has five lensgroups, namely a positive, a negative, a positive, a positive, and anegative lens group, and has a zoom arrangement where, during zooming,all the lens groups are movable. Here, the third lens group Gr3 and thefifth lens group Gr5 are linked together so as to move together. Duringmagnification variation from the wide-angle end (W) to the telephoto end(T), the first lens group Gr1 moves monotonically toward the objectside, the second lens group Gr2 moves first toward the image side, thentoward the object side, and then again toward the image side. The thirdto fifth groups Gr3 to Gr5 move toward the object side and, short of thetelephoto end (T), back toward the image side.

In the seventh embodiment (FIG. 23), the zoom lens system ZL has sixlens groups, namely a positive, a negative, a positive, a positive, anegative, and a positive lens group, and has a zoom arrangement where,during zooming, the first to fifth lens groups Gr1 to Gr5 are movable.Here, the third lens group Gr3 and the fifth lens group Gr5 are linkedtogether so as to move together. During magnification variation from thewide-angle end (W) to the telephoto end (T), the first lens group Gr1moves monotonically toward the object side, the second lens group Gr2moves first toward the object side, then toward the image side, and thenagain toward the object side. The third to fifth groups Gr3 to Gr5 movemonotonically toward the object side.

In the fifth embodiment (FIG. 21), each lens group is composed, in termsof the paraxial surface shapes of the constituent lens elements, asfollows from the object side. The first lens group Gr1 is composed of adoublet lens element made up of a negative meniscus lens element concaveto the image side and a positive meniscus lens element convex to theobject side and a positive meniscus lens element convex to the objectside. The second lens group Gr2 is composed of a negative meniscus lenselement concave to the image side, a biconcave negative lens element, abiconvex positive lens element having aspherical surfaces on both sides,and a doublet lens element (a sub group GrV) made up of a biconcavenegative lens element and a planoconvex positive lens element. The thirdlens group Gr3 is composed of a biconvex positive lens element havingaspherical surfaces on both sides and a doublet lens element made up ofa biconcave negative lens element and a biconvex positive lens element.To the object side of the third lens group Gr3, an aperture stop ST isarranged. The fourth lens group Gr4 is composed of a single biconvexpositive lens element having aspherical surfaces on both sides. Thefifth lens group Gr5 is composed of a single doublet lens element madeup of a biconcave negative lens element and a positive meniscus lenselement convex to the object side.

In the sixth embodiment (FIG. 22), each lens group is composed, in termsof the paraxial surface shapes of the constituent lens elements, asfollows from the object side. The first lens group Gr1 is composed of adoublet lens element made up of a negative meniscus lens element concaveto the image side and a positive meniscus lens element convex to theobject side and a positive meniscus lens element convex to the objectside. The second lens group Gr2 is composed of a negative meniscus lenselement concave to the image side, a biconcave negative lens element, abiconvex positive lens element having aspherical surfaces on both sides,and a negative meniscus lens element concave to the object side (a subgroup GrV). The third lens group Gr3 is composed of a biconvex positivelens element having aspherical surfaces on both sides and a doublet lenselement made up of a biconcave negative lens element and a biconvexpositive lens element. To the object side of the third lens group Gr3,an aperture stop ST is arranged. The fourth lens group Gr4 is composedof a single positive meniscus lens element convex to the image side andhaving aspherical surfaces on both sides. The fifth lens group Gr5 iscomposed of a single biconcave negative lens element.

In the seventh embodiment (FIG. 23), each lens group is composed, interms of the paraxial surface shapes of the constituent lens elements,as follows from the object side. The first lens group Gr1 is composed ofa doublet lens element made up of a negative meniscus lens elementconcave to the image side and a positive meniscus lens element convex tothe object side and a positive meniscus lens element convex to theobject side. The second lens group Gr2 is composed of two negativemeniscus lens elements concave to the image side, a biconvex positivelens element having aspherical surfaces on both sides, and a doubletlens element (a sub group GrV) made up of a biconcave negative lenselement and a planoconvex positive lens element. The third lens groupGr3 is composed of a biconvex positive lens element and a doublet lenselement made up of a biconcave negative lens element and a biconvexpositive lens element. To the object side of the third lens group Gr3,an aperture stop ST is arranged. The fourth lens group Gr4 is composedof a single biconvex positive lens element having aspherical surfaces onboth sides. The fifth lens group Gr5 is composed of a single doubletlens element made up of a biconcave negative lens element and a positivemeniscus lens element convex to the object side. The sixth lens groupGr6 is composed of a single biconvex positive lens element.

EXAMPLES

Hereinafter, the construction and other features ofvariable-magnification optical systems embodying the present inventionwill be described more specifically with reference to the constructiondata and other data of practical examples. Examples 1 to 7 (EX1 to EX7)presented below are numerical examples corresponding to the first toseventh embodiments, respectively, described above. Accordingly, theoptical construction diagrams (FIGS. 1 to 4) showing the first to fourthembodiments also show the lens arrangement, lens shapes, and otherfeatures of the corresponding ones of Examples 1 to 4, and the opticalconstruction diagrams (FIGS. 21 to 23) showing the fifth to seventhembodiments also show the lens arrangement, optical path, and otherfeatures of the corresponding ones of Examples 5 to 7.

In the construction data of each practical example, listed as surfacedata are, from left to right, surface number, radius of curvature r(mm), axial surface-to-surface distance d (mm), refractive index nd forthe d-line (with a wavelength of 587.56 nm), and Abbe number vd for thed-line. A surface whose surface number is marked with an asterisk “*” isan aspherical surface, of which the surface shape is defined by formula(AS) below in a local rectangular coordinate system (x, y, z) having itsorigin at the vertex of the surface. Listed as aspherical surface dataare aspherical surface coefficients etc. In the aspherical surface dataof each practical example, any absent term indicates that thecorresponding coefficient equals zero, and throughout the data, “E−n”stands for “×10^(−n).”

$\begin{matrix}{z = {{\left( {c \cdot h^{2}} \right)/\left\{ {1 + \sqrt{\left\lbrack {1 - {\left( {1 + K} \right) \cdot c^{2} \cdot h^{2}}} \right\rbrack}} \right\}} + {\sum\left( {{Aj} \cdot h^{j}} \right)}}} & ({AS})\end{matrix}$

where

-   -   h represents the height in the direction perpendicular to the        z-axis (optical axis AX) (h²=x²+y²);    -   z represents the amount of sag in the optical axis AX direction        at the height h (relative to the vertex of the surface)    -   c represents the curvature (the reciprocal of the radius of        curvature) at the vertex of the surface;    -   K represents a conic constant; and    -   Aj represents the aspherical surface coefficient of order j.

Listed as miscellaneous data are zoom ratio and, for each of thedifferent focal length conditions W, M, and T, focal length (f, mm) ofthe entire system, f-number (FNO), half-angle of view (ω, °), imageheight (Y′, mm), total lens length (TL, mm), backfocus (BF, mm), andvariable surface-to-surface distance di (where i represents the surfacenumber, mm). Listed as zooming group data are the focal lengths of therespective lens groups (f1, f2, f3, f4, f5, f6; mm). Here, the backfocusBF denotes the distance from the image-side surface of theplane-parallel plate PT to the image surface IM, and the total lenslength TL denotes the distance from the foremost surface of the lenssystem to the image surface IM. Tables 1 and 3 list data related to therelevant formulae in each practical example, and Tables 2 and 4 listvalues corresponding to the relevant formulae in each practical example.

FIGS. 5A-5I, FIGS. 6A-6I, FIGS. 7A-7I, and FIGS. 8A-8I are longitudinalaberration diagrams (in ordinary condition (without decentering),focused at infinity) corresponding to Examples 1 to 4 (EX1 to EX4)respectively, FIGS. 5A-5C, 6A-6C, 7A-7C, and 8A-8C showing theaberrations observed at the wide-angle end (W), FIGS. 5D-5F, 6D-6F,7D-7F, and 8D-8F showing the aberrations observed at the middle focallength (M), and FIGS. 5G-5I, 6G-6I, 7G-7I, and 8G-8I showing theaberrations observed at the telephoto end (T). Of these diagrams, FIGS.5A, 5D, 5G, 6A, 6D, 6G, 7A, 7D, 7G, 8A, 8D, and 8G are sphericalaberration diagrams, FIGS. 5B, 5E, 5H, 6B, 6E, 6H, 7B, 7E, 7H, 8B, 8E,and 8H are astigmatism diagrams, and FIGS. 5C, 5F, 51, 6C, 6F, 6I, 7C,7F, 7I, 8C, 8F, and 8I are distortion diagrams.

In spherical aberration diagrams, a solid line represents the amount ofspherical aberration for the d-line (with a wavelength of 587.56 nm), adash-and-dot line represents the amount of spherical aberration for theC-line (with a wavelength of 656.28 nm), and a broken line representsthe amount of spherical aberration for the g-line (with a wavelength of435.84 nm), all in terms of deviations (mm) from the paraxial imagesurface in the optical axis AX direction, the vertical axis representingthe height of incidence at the pupil as normalized with respect to themaximum height of incidence (hence, the relative height at the pupil).In astigmatism diagrams, a broken line T represents the tangential imagesurface for the d-line, and a solid line S represents the sagittal imagesurface for the d-line, both in terms of deviations (mm) from theparaxial image surface in the optical axis AX direction, the verticalaxis representing the image height (IMG HT, in mm). In distortiondiagrams, the horizontal axis represents the distortion (%) for thed-line, and the vertical axis represents the image height (IMG HT, inmm). The maximum value of the image height IMG HT corresponds toone-half of the diagonal length of the light-receiving surface SS of theimage sensing device SR.

FIGS. 9A-9F, 10A-10F, and 11A-11F, FIGS. 12A-12F, 13A-13F, and 14A-14F,FIGS. 15A-15F, 16A-16F, and 17A-17F, and FIGS. 18A-18F, 19A-19F, and20A-20F are lateral aberration diagrams corresponding to Examples 1 to 4(EX1 to EX4) respectively, showing the lateral aberrations (mm) observedin ordinary condition (without decentering) in each of the differentfocal length conditions W, M, and T. Of these diagrams, FIGS. 9A-9C,10A-10C, and 11A-11C, FIGS. 12A-12C, 13A-13C, and 14A-14C, FIGS.15A-15C, 16A-16C, and 17A-17C, and FIGS. 18A-18C, 19A-19C, and 20A-20Cshow the lateral aberrations in tangential rays, and FIGS. 9D-9F,10D-10F, and 11D-11F, FIGS. 12D-12F, 13D-13F, and 14D-14F, FIGS.15D-15F, 16D-16F, and 17D-17F, and FIGS. 18D-18F, 19D-19F, and 20D-20Fshow the lateral aberrations in sagittal rays. Here, the lateralaberrations observed at the image height ratio (half-angle of view ω°)indicated under RELATIVE FIELD HEIGHT are represented by a solid linefor the d-line (with a wavelength of 587.56 nm), by a dash-and-dot linefor the C-line (with a wavelength of 656.28 nm), and by a broken linefor the g-line (with a wavelength of 435.84 nm). An image height ratiois a relative image height obtained by normalizing an image height withrespect to the maximum image height Y′.

FIGS. 24A-24I, FIGS. 25A-25I, and FIGS. 26A-26I are aberration diagrams(in ordinary condition (without decentering), focused at infinity)corresponding to Examples 5 to 7 (EX5 to EX7) respectively, FIGS.24A-24C, 25A-25C, and 26A-26C showing the aberrations observed at thewide-angle end (W), FIGS. 24D-24F, 25D-25F, and 26D-26F showing theaberrations observed at the middle focal length (M), and FIGS. 24G-24I,25G-25I, FIGS. 26G-26I showing the aberrations observed at the telephotoend (T) (the diagrams suffixed with “A,” “D,” and “G” showing sphericalaberrations etc., the diagrams suffixed with “B,” “E,” and “H” showingastigmatism, and the diagrams suffixed with “C,” “F,” and “I” showingdistortion). In these diagrams, FNO represents f-number, and Y′ (mm)represents the maximum image height on the light-receiving surface SS ofthe image sensing device SR (corresponding to the distance from theoptical axis AX). In spherical aberration diagrams, a solid line d, adash-and-dot line g, and a dash-dot-dot line c represent the sphericalaberration (mm) for the d-, g-, and c-lines respectively, and a brokenline SC represent the deviation (mm) from the sine condition. Inastigmatism diagrams, a broken line DM represents the meridional imagesurface, and a solid line DS represents a sagittal image surface, eachrepresenting the astigmatism (mm) for the d-line. In distortiondiagrams, a solid line represents the distortion (%) for the d-line.

FIGS. 27A-27E and 28A-28E, FIGS. 29A-29E and 30A-30E, and FIGS. 31A-31Eand 32A-32E are lateral aberration diagrams of Examples 5 to 7 (EX5 toEX7), respectively, without decentering (in ordinary condition) and withdecentering (during camera shake correction), all with focus atinfinity. FIGS. 27A-27E and 28A-28E correspond to Example 5, FIGS.29A-29E and 30A-30E correspond to Example 6, and FIGS. 31A-31E and32A-32E correspond to Example 7. Of these diagrams, FIGS. 27A, 27B, 28A,28B, 29A, 29B, 30A, 30B, 31A, 31B, 32A, and 32B are lateral aberrationdiagrams without decentering, and FIGS. 27C-27E, 28C-28E, 29C-29E,30C-30E, 31C-31E, and 32C-32E are lateral aberration diagrams withdecentering (y′ (mm) represents the image height on the light-receivingsurface SS of the image sensing device SR (corresponding to the distancefrom the optical axis AX)). FIGS. 27A-27E, 29A-29E, and 31A-31E show thedegradation in axial and off-axial lateral aberrations observed whenimage blur of an angle of 0.3 degrees is corrected by decentering thedecenterable lens component (that is, the sub group (vibrationcorrection group) GrV) at the wide-angle end (W), and FIGS. 28A-28E,30A-30E, and 32A-32E show the degradation in axial and off-axial lateralaberrations observed when image blur of an angle of 0.3 degrees iscorrected by decentering the decenterable lens component at thetelephoto end (T).

Example 1

Unit: mm Surface Data Surface No. r d nd vd  1 53.353 1.200 1.8467 23.78 2 34.674 6.416 1.4970 81.61  3 402.870 0.100  4 38.442 4.236 1.696855.46  5 191.178 d5   6 312.305 0.800 1.9108 35.25  7 11.384 4.798  8−33.732 0.800 1.7725 49.62  9 34.947 0.100 10 21.959 3.793 1.8467 23.7811 −24.154 0.854 12 −18.083 0.800 1.8348 42.72 13 −130.439 d1314(Aperture) ∞ 0.100 15* 15.000 2.454 1.7308 40.50 16* −64.765 3.097 17−97.252 0.800 1.9037 31.31 18 11.577 4.360 1.4970 81.61 19 −12.667 d1920* −968.683 3.846 1.5831 59.38 21* −35.765 d21 22 −66.082 0.800 1.834842.72 23 22.247 d23 24 35.757 2.171 1.6727 32.17 25 −658.266 13.500  26∞ 4.200 1.5168 64.20 27 ∞ BF Aspherical Surface Data K A4 A6 A8 Surface15 0.00000 7.4222E−06 −9.8313E−09 1.9918E−09 Surface 16 0.000008.6528E−05 −1.1015E−08 −1.3227E−10 Surface 20 0.00000 −1.1988E−04−9.3860E−07 0.0000E+00 Surface 21 0.00000 −1.2049E−04 −6.4789E−070.0000E+00 Miscellaneous Data Zoom Ratio 6.95 Wide (W) Mid (M) Tele (T)Focal Length 14.260 37.580 99.050 F-number 3.500 5.000 5.600 Half-Angleof View (°) 37.186 16.056 6.231 Image Height 9.717 11.198 11.406 TotalLens Length 94.980 98.931 109.980 BF 1.050 1.050 1.050 d5 2.000 14.27726.978 d13 23.992 8.813 2.000 d19 2.489 3.893 13.003 d21 2.594 7.3082.000 d23 3.630 4.364 5.723 Zoom Lens Group Data Group Starting SurfaceFocal Length 1 1 53.023 2 6 −10.787 3 15 19.161 4 20 63.589 5 22 −19.8556 24 50.479

Example 2

Unit: mm Surface Data Surface No. r d nd vd  1 45.466 1.200 1.8467 23.78 2 31.613 5.943 1.4970 81.61  3 250.961 0.100  4 44.010 3.874 1.696855.46  5 226.794 d5   6 −851.489 0.800 1.9108 35.25  7 10.873 4.711  8−35.933 0.800 1.8042 46.50  9 443.298 0.166 10 20.941 2.943 1.9229 20.8811 −82.200 0.800 1.8348 42.72 12 37.313 d12 13(Aperture) ∞ 0.100 14*16.355 4.031 1.7308 40.50 15* −24.902 2.084 16 −24.142 1.883 1.903731.31 17 13.821 6.282 1.4970 81.61 18 −11.790 d18 19* −802.917 4.2001.5891 61.25 20* −35.420 d20 21 −86.192 0.800 1.8348 42.72 22 21.0503.674 23 44.976 2.646 1.6730 38.15 24 −88.794 d24 25 ∞ 4.200 1.516864.20 26 ∞ BF Aspherical Surface Data K A4 A6 A8 Surface 14 0.00000−5.4651E−06 1.0123E−07 9.6859E−09 Surface 15 0.00000 8.2055E−051.3694E−07 9.7214E−09 Surface 19 0.00000 −1.1413E−04 −7.1734E−070.0000E+00 Surface 20 0.00000 −1.1072E−04 −4.8996E−07 0.0000E+00Miscellaneous Data Zoom Ratio 6.95 Wide (W) Mid (M) Tele (T) FocalLength 14.260 37.590 99.060 F-number 3.600 5.000 5.500 Half-Angle ofView (°) 37.182 16.053 6.231 Image Height 9.721 11.319 11.684 Total LensLength 99.643 102.280 113.387 BF 1.050 1.050 1.050 d5 2.249 14.24328.562 d12 26.227 8.973 2.081 d18 2.373 4.308 14.711 d20 2.805 8.1792.115 d24 13.702 14.289 13.631 Zoom Lens Group Data Group StartingSurface Focal Length 1 1 55.083 2 6 −11.414 3 14 20.822 4 19 62.771 5 21−44.660

Example 3

Unit: mm Surface Data Surface No. r d nd vd  1 55.637 1.200 1.8467 23.78 2 35.997 5.169 1.4970 81.61  3 688.516 0.100  4 41.080 4.006 1.696855.46  5 195.320 d5   6 −454.535 0.800 1.9108 35.25  7 10.583 4.625  8−30.504 0.800 1.8810 40.14  9 29.951 0.100 10 22.006 2.919 1.9229 20.8811 −61.375 d11 12(Aperture) ∞ 0.100 13* 15.660 4.639 1.7308 40.50 14*−48.995 2.624 15 −48.941 0.800 1.9037 31.31 16 12.525 7.782 1.4970 81.6117 −12.999 d17 18* −940.006 4.200 1.5831 59.46 19* −36.781 d19 20−54.041 0.800 1.8830 40.80 21 22.058 1.000 1.4970 81.61 22 23.898 1.94823 29.826 2.894 1.6541 39.68 24 −131.437 d24 25 ∞ 4.200 1.5168 64.20 26∞ BF Aspherical Surface Data K A4 A6 A8 Surface 13 0.00000 1.6992E−051.5202E−07 1.0224E−08 Surface 14 0.00000 9.3824E−05 3.0875E−071.2966E−08 Surface 18 0.00000 −1.0940E−04 −6.1173E−07 0.0000E+00 Surface19 0.00000 −1.0586E−04 −4.3117E−07 0.0000E+00 Miscellaneous Data ZoomRatio 6.95 Wide (W) Mid (M) Tele (T) Focal Length 14.260 37.580 99.050F-number 3.600 5.000 5.500 Half-Angle of View (°) 37.185 16.056 6.231Image Height 9.720 11.078 11.484 Total Lens Length 99.980 103.937113.974 BF 1.050 1.050 1.050 d5 2.301 13.711 30.225 d11 26.501 8.8312.045 d17 2.392 3.802 14.447 d19 3.530 8.133 2.000 d24 13.500 17.70313.500 Zoom Lens Group Data Group Starting Surface Focal Length 1 155.323 2 6 −11.763 3 13 21.854 4 18 65.531 5 20 −40.815

Example 4

Unit: mm Surface Data Surface No. r d nd vd  1 55.068 1.200 1.8467 23.78 2 35.333 5.320 1.4970 81.61  3 482.141 0.100  4 39.209 4.129 1.696855.46  5 183.047 d5   6 −6788.303 0.800 1.8830 40.80  7 10.292 4.753  8−34.335 0.800 1.8830 40.80  9 32.325 0.100 10 21.895 2.847 1.9229 20.8811 −104.275 d11 12(Aperture) ∞ 0.100 13* 15.819 4.124 1.7308 40.50 14*−50.999 2.696 15 −38.375 0.800 1.9037 31.31 16 13.826 6.345 1.4970 81.6117 −12.402 d17 18* 224178.550 4.200 1.5831 59.46 19 −33.203 2.000 1.882037.22 20* −34.848 d20 21 −45.157 0.800 1.8830 40.80 22 24.457 0.9631.4970 81.61 23 23.855 1.604 24 28.021 3.034 1.6541 39.68 25 −101.530d25 26 ∞ 4.200 1.5168 64.20 27 ∞ BF Aspherical Surface Data K A4 A6 A8Surface 13 0.00000 2.0212E−05 4.4038E−07 1.2928E−08 Surface 14 0.000009.6020E−05 7.0304E−07 1.6560E−08 Surface 18 0.00000 −8.8546E−052.7168E−08 0.0000E+00 Surface 20 0.00000 −5.0144E−05 0.0000E+000.0000E+00 Miscellaneous Data Zoom Ratio 6.95 Wide (W) Mid (M) Tele (T)Focal Length 14.260 37.580 99.060 F-number 3.600 5.000 5.500 Half-Angleof View (°) 37.184 16.054 6.231 Image Height 9.729 11.008 11.383 TotalLens Length 99.980 104.333 113.986 BF 1.050 1.050 1.050 d5 2.178 13.39129.559 d11 26.288 9.032 2.379 d17 2.387 4.195 14.395 d20 3.661 8.0612.000 d25 13.500 17.688 13.688 Zoom Lens Group Data Group StartingSurface Focal Length 1 1 55.323 2 6 −11.763 3 13 21.854 4 18 65.531 5 21−40.815

Example 5

Unit: mm Surface Data Surface No. r d nd vd  1 48.898 1.800 1.8466623.78  2 32.654 6.169 1.49700 81.61  3 272.082 0.300  4 32.035 4.5721.69680 55.48  5 109.041 Variable  6 269.010 1.200 1.91082 35.25  79.488 5.286  8 −219.618 0.800 1.77250 49.65  9 25.498 0.504 10* 23.2232.903 1.84666 23.78 11* −80.599 1.000 12 −46.624 0.800 1.83481 42.72 1333.992 1.609 1.84666 23.78 14 ∞ Variable 15(Aperture) ∞ 0.930 16* 10.6183.818 1.73077 40.50 17* −82.008 1.817 18 −89.945 1.057 1.90366 31.31 197.459 4.867 1.49700 81.61 20 −24.493 Variable 21* 30.345 2.867 1.5831359.38 22* −51.375 Variable 23 −72.731 1.000 1.83481 42.72 24 20.0481.834 1.67270 32.17 25 73.090 Variable 26 ∞ 4.200 1.51680 64.20 27 ∞ BFAspherical Surface Data K A4 A6 A8 Surface 10 0.00000 −2.26008E−06−1.12461E−07 −7.12245E−09 Surface 11 0.00000 −4.13799E−05 −1.90824E−07−8.43392E−09 Surface 16 0.00000 −3.83814E−05 −1.45574E−08 4.00546E−09Surface 17 0.00000 3.32806E−05 3.50436E−07 2.45802E−09 Surface 210.00000 −8.40535E−05 −2.14381E−06 Surface 22 0.00000 −8.48713E−05−2.02828E−06 Miscellaneous Data Zoom Ratio 7.143 Wide (W) Mid (M) Tele(T) Focal Length 14.000 37.422 100.000 F-number 3.600 5.000 5.700Half-Angle of View (°) 37.686 16.119 6.173 Image Height 9.704 10.85410.984 Total Lens Length 95.044 104.622 115.000 BF 1.076 1.054 0.991 d51.324 12.639 24.576 d14 21.043 8.844 1.970 d20 7.911 6.367 8.513 d222.802 4.346 2.200 d25 11.554 22.038 27.417 Zoom Lens Group Data GroupStarting Surface Focal Length 1 1 49.663 2 6 −10.103 3 15 22.659 4 2133.143 5 23 −34.395

Example 6

Unit: mm Surface Data Surface No. r d nd vd  1 46.831 1.800 1.8466623.78  2 31.030 5.572 1.49700 81.61  3 179.398 0.300  4 27.841 4.5711.69680 55.48  5 87.175 Variable  6 156.065 1.200 1.91082 35.25  7 9.2475.536  8 −39.150 0.800 1.77250 49.65  9 23.322 0.501 10* 22.052 2.9741.84666 23.78 11* −42.991 1.000 12 −35.026 0.800 1.49700 81.61 13−152.535 Variable 14(Aperture) ∞ 0.930 15* 10.953 2.612 1.73077 40.5016* −76.558 1.646 17 −324.973 1.001 1.90366 31.31 18 7.913 4.597 1.4970081.61 19 −21.398 Variable 20* −65.511 2.648 1.58313 59.38 21* −18.281Variable 22 −30.571 1.000 1.83481 42.72 23 1223.683 Variable 24 ∞ 4.2001.51680 64.20 25 ∞ BF Aspherical Surface Data K A4 A6 A8 Surface 100.00000 3.46391E−06 1.77182E−07 −1.29219E−08 Surface 11 0.00000−2.40172E−05 1.56016E−07 −1.33631E−08 Surface 15 0.00000 −3.55272E−05−1.25475E−07 1.16889E−08 Surface 16 0.00000 4.25279E−05 2.18514E−076.64296E−09 Surface 20 0.00000 −1.55759E−04 −3.96523E−06 Surface 210.00000 −1.06996E−04 −2.97413E−06 Miscellaneous Data Zoom Ratio 5.000Wide (W) Mid (M) Tele (T) Focal Length 14.000 31.300 70.000 F-number3.600 5.000 5.700 Half-Angle of View (°) 37.686 19.061 8.783 ImageHeight 9.696 10.765 10.980 Total Lens Length 87.458 91.726 100.000 BF1.076 1.055 0.991 d5 1.272 6.723 20.278 d13 19.335 6.960 1.970 d19 8.0046.147 7.344 d21 2.803 4.660 3.463 d23 11.281 22.494 22.266 Zoom LensGroup Data Group Starting Surface Focal Length 1 1 47.089 2 6 −10.516 314 20.050 4 20 42.604 5 22 −35.715

Example 7

Unit: mm Surface Data Surface No. r d nd vd  1 49.692 1.800 1.8466623.78  2 33.275 6.163 1.49700 81.61  3 338.133 0.300  4 33.430 4.4691.69680 55.48  5 121.392 Variable  6 900.526 1.200 1.91082 35.25  79.533 4.966  8 376.111 0.800 1.77250 49.65  9 28.891 0.602 10* 28.6932.799 1.84666 23.78 11* −64.608 1.000 12 −39.469 0.800 1.83481 42.72 1326.388 1.835 1.84666 23.78 14 ∞ Variable 15(Aperture) ∞ 0.930 16* 10.7223.391 1.73077 40.50 17* −91.497 2.011 18 −107.198 1.143 1.90366 31.31 197.485 4.661 1.49700 81.61 20 −31.084 Variable 21* 33.824 2.923 1.5831359.38 22* −45.302 Variable 23 −68.702 1.000 1.80420 46.49 24 61.2911.094 1.78472 25.72 25 75.683 Variable 26 7769.088 1.159 1.83481 42.7227 −331.545 11.250  28 ∞ 4.200 1.51680 64.20 29 ∞ BF Aspherical SurfaceData K A4 A6 A8 Surface 10 0.00000 9.15770E−07 −2.01406E−07 −4.84394E−09Surface 11 0.00000 −5.00636E−05 −3.22182E−07 −6.52489E−09 Surface 160.00000 −3.91008E−05 −2.99751E−08 2.32568E−09 Surface 17 0.000002.48704E−05 2.47912E−07 1.66315E−09 Surface 21 0.00000 −7.22289E−05−1.94517E−06 Surface 22 0.00000 −6.45725E−05 −1.84095E−06 MiscellaneousData Zoom Ratio 7.143 Wide (W) Mid (M) Tele (T) Focal Length 14.00037.420 100.000 F-number 3.600 5.003 5.700 Half-Angle of View (°) 37.68616.120 6.173 Image Height 9.699 10.857 10.980 Total Lens Length 96.397110.203 120.000 BF 1.076 1.056 0.991 d5 1.416 12.773 24.705 d14 20.6049.508 1.970 d20 8.209 8.158 9.517 d22 3.680 3.732 2.373 d25 0.916 14.48219.948 Zoom Lens Group Data Group Starting Surface Focal Length 1 149.772 2 6 −10.075 3 15 24.045 4 21 33.667 5 23 −44.370 6 26 380.920

TABLE 1 Related Data Example 1 Example 2 Example 3 Example 4 f1 53.0255.08 55.32 54.58 f2 −10.79 −11.41 −11.76 −11.71 f3 19.16 20.82 21.8621.83 f4 63.59 62.77 65.53 60.41 fv −19.86 −20.20 −18.06 −17.56 R5A−66.08 −86.19 −54.04 −45.16 R5B 22.25 21.05 23.90 23.85 R4A −968.68−802.92 −940.01 2.242E+05 R4B −35.77 −35.42 −36.78 −34.85

TABLE 2 Values of Formulae Example 1 Example 2 Example 3 Example 4 (1)|f1/f2| 4.91 4.83 4.70 4.66 (2) f4/f1 1.20 1.14 1.18 1.11 (3) |f4/fv|3.20 3.11 3.63 3.44 (4) f4/f3 3.32 3.01 3.00 2.77 (5) (R5A + R5B)/ 0.500.61 0.39 0.31 (R5A − R5B) (6) (R4A + R4B)/ 1.08 1.09 1.08 1.00 (R4A −R4B)

TABLE 3 Related Data Example 5 Example 6 Example 7 M 2 1 2 N 5 4 5 fv−56.967 −91.689 −48.314 f2 −10.103 −10.516 −10.075 rA −46.624 −35.026−39.469 rB ∞ −152.535 ∞ ft 100.000 70.000 100.000 Ymax 10.815 10.81510.815 Vd — 81.610 — f5 −34.395 −35.715 −44.370 f3 22.659 20.050 24.045M5 15.261 10.985 19.032 f4 33.143 42.604 33.667 M4 15.863 11.645 17.725

TABLE 4 Values of Formulae Example 5 Example 6 Example 7  (7) M/N 0.400.25 0.40  (8) fv/f2 5.64 8.72 4.80  (9) (rA + rB)/(rA − rB) −1.00 −1.60−1.00 (10) ft/Ymax 9.25 6.47 9.25 (11) Vd — 81.61 — (12) f5/f3 −1.52−1.78 −1.85 (13) M5/f5 −0.44 −0.31 −0.43 (14) f4/f3 1.46 2.12 1.40 (15)M4/M5 1.04 1.06 0.93

What is claimed is:
 1. A variable-magnification optical systemcomprising, from an object side, a first lens group having a positiveoptical power, a second lens group having a negative optical power, athird lens group having a positive optical power, a fourth lens grouphaving a positive optical power, and a fifth lens group having anegative optical power, the variable-magnification optical systemachieving magnification variation from a wide-angle end to a telephotoend by varying all axial distances between the lens groups, thevariable-magnification optical system achieving focusing by moving thefourth lens group as a focusing group toward the object side, thevariable-magnification optical system achieving vibration correction bymoving all or part of the fifth lens group as a vibration correctiongroup in a direction perpendicular to an optical axis, wherein Formulae(1) to (3) below are fulfilled:4.0<|f1/f2|<6.0  (1)1.0<f4/f1<1.5  (2)2.0<|f4/fv|<4.0  (3) where f1 represents a focal length of the firstlens group; f2 represents a focal length of the second lens group; f4represents a focal length of the fourth lens group; and fv represents afocal length of the vibration correction group.
 2. Thevariable-magnification optical system according to claim 1, whereinFormula (4) below is fulfilled:2.5<f4/f3<4.5  (4) where f3 represents a focal length of the third lensgroup.
 3. The variable-magnification optical system according to claim1, wherein an aperture stop is arranged between the second and thirdlens groups.
 4. The variable-magnification optical system according toclaim 1, wherein the vibration correction group is composed of a singlelens element or a doublet lens element made up of a positive lenselement and a negative lens element.
 5. The variable-magnificationoptical system according to claim 1, wherein Formula (5) below isfulfilled:0.1<(R5A+R5B)/(R5A−R5B)<0.70  (5) where R5A represents a radius ofcurvature of a surface arranged at a most object-side position in thevibration correction group; and R5B represents a radius of curvature ofa surface concave to an image side in the vibration correction group. 6.The variable-magnification optical system according to claim 1, whereinFormula (6) below is fulfilled:1.0<(R4A+R4B)/(R4A−R4B)<1.2  (6) where R4A represents a radius ofcurvature of a most object-side surface in the fourth lens group; andR4B represents a radius of curvature of a most image-side surface in thefourth lens group.
 7. An imaging optical device comprising thevariable-magnification optical system according to claim 1 and an imagesensing device for converting an optical image formed on alight-receiving surface thereof into an electrical signal, wherein thevariable-magnification optical system is arranged such that an opticalimage of a subject is formed on the light-receiving surface of the imagesensing device.
 8. A digital appliance comprising the imaging opticaldevice according to claim 7 so as to additionally have at least one of afunction of taking a still image of a subject and a function of taking amoving image of a subject.